Digestion Biology 1st years notes fa fsc chapter no 11 short questions, long question, Contains solved exercises, review questions, MCQs, important board questions and chapter overview.
Class 11 Biology Notes Short Question 2021
Q.2 i) What do you mean by physical digestion?
Physical digestion (Mechanical digestion):
Physical digestion involves physically breaking the food into smaller pieces. Mechanical digestion begins in the mouth as the food is chewed. Chemical digestion involves breaking down the food into simpler nutrients that can be used by the cells. Chemical digestion begins in the mouth when food mixes with saliva. The physical breakdown of the food also increases the available surface area for the action of the digestive enzymes.
Q.2 ii) Name the cells that secrete mucus. What are the functions of mucus?
Special cells secrete a protective coating called mucus, on the stomach walls to prevent damage from gastric acids.
Functions of mucus:
- Mucus, viscous fluid that moistens, lubricates and protects many of the passages of the digestive and respiratory tracts in the body. Mucus is composed of water, epithelial (surface) cells, dead leukocytes, mucin, and inorganic salts.
- The stomach also has large numbers of mucous cells. Gastric mucus forms a layer about one millimetre thick that lines the stomach, protecting the organ from highly acidic gastric juice and preventing the juice from digesting the stomach itself.
Q.2 iii) If a major part of the small intestine of mammals is removed, will this affect the absorption of food?
The small intestine is the part of the intestines where 90% of the digestion and absorption of food occurs. The small intestine is about 17 feet long. The food from the stomach becomes thoroughly liquefied, it passes into the duodenum, the first segment of the small intestine. If only one small section of the small intestine is removed, absorption will be quite minimal after the immediate recovery period. The risk comes when a large section of the small intestine is removed, with increasingly shorter segments of intestine left to digest food. The small intestine contains villi in which absorption takes place. As most of the part of an intestine is removed so less absorption and digestion of food takes place. At this point, nutrition can become a big issue, as both micronutrients and calories are not absorbed well.
Q.2 iv) Name the different parts of the large intestine of humans in their natural sequence.
Parts of the large intestine:
The large intestine is made up of three parts:
- The cecum is a pouch at the beginning of the large intestine that joins the small intestine to the large intestine.
- The colon extends from the cecum up the right side of the abdomen, across the upper abdomen, and then down the left side of the abdomen, finally connecting to the rectum.
- The rectum is where faeces are stored until they leave the digestive system through the anus as a bowel movement.
Q.2 v) What is the advantage of emulsification of fats by bile juice?
Bile is stored and concentrated in the gallbladder. The presence of fats in the gut during meals stimulates the gallbladder to empty. Bile enters the duodenum emulsifying fats into smaller globules, which can then be broken down further by lipase enzymes. Bile has detergent-like action on particles of dietary fat which causes fat globules to break down or emulsify into the minute, microscopic droplets. Emulsification is of great importance because it greatly increases the surface area of fat, making it available for digestion by lipases, which cannot access the inside of lipid droplets.
Q.2 vi) Name the largest gland of the human body and where is it located?
The liver is the largest and most important organ in the human body.
It is located in a central position of the abdomen and is most closely involved in almost all physiological activities.
What are the main symptoms of dyspepsia?
Symptoms of dyspepsia:
The symptoms of dyspepsia may include pain in the upper abdomen, often made worse by eating and nausea, particularly in the morning. Patients with non-ulcer dyspepsia often experience these symptoms several times a week for months.
Q.2 viii) What measures are to be adopted for the diagnosis of anorexia nervosa?
1. Physical examination:
This may include measuring height and weight; checking patient vital signs, such as heart rate, blood pressure and temperature; skin and nails for problems; and examining your abdomen.
2. Lab tests:
These may include a complete blood count (CBC) and more specialized blood tests to check electrolytes and protein as well as the functioning of liver, kidney and thyroid. A urinalysis also may be done.
3. Psychological evaluation:
A doctor or psychiatrist will likely evaluate patients’ thoughts, feelings and eating habits. The person with anorexia needs to be actively involved in the treatment.
Biology Class 11 Notes Long Question 2021
Q.3 i) Explain the role of the nervous system and gastrin hormone on the secretion of gastric juice.
Role of the nervous system in the secretion of gastric juice:
Sometimes even the sight, smell, taste or hearing of delicious food, stimulate the nervous system which orders for the secretion of a small amount of gastric juice like watering of mouth. This is proved by the experiment of Russian. Pavlov. He cut the oesophagus of a dog and left the cut end open to the outside. When he fed this dog, the food, of course, never reached the stomach, yet the stomach resulted in the secretion of about one fourth the normal amount of gastric juice. This showed that the gastric secretion was under the reflex control and cutting off the gastric nerves proved it. If there are more proteins in the food, a message is given to the brain which in result would order the gastric glands to secrete more gastric juice.
Role of gastrin hormone:
A hormone called gastrin controls the secretion of gastric juice. Protein molecules stimulate the endocrine cells of the stomach to secrete gastrin. The liberating gastrin is soon absorbed by the blood which carries it to the gastric glands to secrete a large amount of gastric juice in the stomach. The contact of the food with the lining of the stomach also causes the cells to secrete gastrin which stimulated the gastric glands to secrete gastric juice.
Q.3 ii) Describe the mechanism of digestion in the stomach.
Mechanism of digestion in the stomach:
Food enters the stomach from the oesophagus through the lower oesophagal sphincter. The stomach is the part where the physical and chemical breakdown of food begins.
Stomach operates like a food mixer, churning the food bolus to a pulp called chyme and releasing numerous chemicals such as digestive hormones, enzymes and gastric juices which help to break down food molecules in the chyme into small particles for absorption into the bloodstream.
A capacity of the stomach:
An empty stomach has a volume of approximately 50 ml. But typically after a meal, its capacity expands to about 1 litre of food and may expand to hold as much as 4 litres. The chyme slowly exits the stomach via the pyloric sphincter or valve and passes into the duodenum.
Structure of the Stomach:
The stomach is J-shaped like structure which looks like a large stretchy bag situated in the middle of the chest behind the liver, between the oesophagus and the first section of the small intestine (the duodenum).
Divisions of the stomach:
The stomach is subdivided into 4 regions each with different cells and gastric functions:
i) Cardiac region:
The Cardiac region, where the contents of the oesophagus empty into the stomach through the lower oesophagal or cardiac sphincter
The fundus is an expanded area curving up above the oesophagal opening.
iii) Body of the stomach:
The body is the central and largest region of the stomach.
Pylorus is the narrow end of the stomach that joins the small intestine at the pyloric sphincter.
Like the cardiac sphincter, the pyloric sphincter is a ring of muscle that regulates the movement of food out of the stomach.
Gastric glands of the stomach:
The wall of the stomach is lined with millions of gastric glands, which together secrete 400-800 ml of gastric juice at each meal. Several kinds of cells are found in the gastric glands.
- 1. Parietal cells
- 2. Chief cells
- 3. mucus-secreting cells
- 4. Hormone-secreting (endocrine) cells
1. Parietal cells:
Parietal cells secrete hydrochloric acid and an intrinsic factor.
a. Hydrochloric acid (HCI):
Parietal cells contain H+ ATPase. This transmembrane protein secretes H+ ions (protons) by active transport, using the energy of ATP. The concentration of H+ ions in the gastric juice can be as high as 0.15 M, giving gastric juice a pH somewhat less than 1
b. Intrinsic factor:
Intrinsic factor is a protein that binds ingested vitamin B and enables it to be absorbed by the intestine.
2. Chief cells:
The chief cells synthesize and secrete pepsinogen, the precursor to the proteolytic enzyme pepsin.
3. mucus-secreting cells:
Special cells secrete a protective coating called mucus, on the stomach walls to prevent damage from gastric acids. Originally it was thought that peptic ulcers were caused by an erosion of this mucus lining by these acids. However recent research indicates that these ulcers are caused largely by the spread of a type of bacteria called Helicobacter pylori bacterium into the gastric walls.
4. hormone-secreting cells:
Secretion by the gastric glands is stimulated by the hormone gastrin. Gastrin is released by endocrine cells in the stomach in response to the arrival of food.
Absorption of food in the stomach:
Very little absorption occurs in the stomach. However, some amount of water, certain ions, and drugs like aspirin and ethanol are absorbed from the stomach into the blood.
Functions of the Stomach:
Although it is a very complex organ which performs a wide variety of digestive actions, the stomach has 3 main functions:
1- Food storage:
Stomach stores the food for a longer time, which allows to eat a larger quantity of food in a relatively short time and then digest it over a longer period.
2. Breakdown of protein and fats:
The stomach breaks down large fat and protein molecules in food, so they can be absorbed in the small intestine. To do this, the stomach releases some powerful gastric juices containing hydrochloric acid and other digestive enzymes. In addition to breaking down food, these acidic juices (pH 1-3) also kill bacteria in the food. For easier digestion, powerful muscles in the stomach wall churn the food into a paste of porridge-like consistency, called chyme. This churning action also ensures that the secreted gastric acids and enzymes are thoroughly mixed with the food.
3- Passage of chyme into the duodenum:
The stomach empties the partially digested chyme into the duodenum (the first segment of the small intestine) at a manageable speed, through the pyloric sphincter. While the intestine is full and still digesting food, the stomach acts as a storage area for food. The absorption of food and water by the stomach is negligible, but iron and highly fat-soluble substances like alcohol are absorbed directly.
Mechanism of Secretion of gastric juice:
The secretion of gastric juice is under reflex control. If there are more proteins in the food, a message is given to the brain which in result would order the gastric glands to secrete more gastric juice. A hormone called gastrin controls the secretion of gastric juice. Protein molecules stimulate the endocrine cells of the stomach to secrete gastrin. The liberating gastrin is soon absorbed by the blood which carries it to the gastric glands to secrete a large amount of gastric juice in the stomach. The contact of the food with the lining of the stomach also causes the cells to secrete gastrin which stimulated the gastric glands to secrete gastric juice.
Q.3 iii) Describe the composition of bile and relate the constituents with respective roles.
Composition of bile:
Bile consists of water, bile, salts, cholesterol, phospholipids, electrolytes and bile pigments which give it its typical yellowish-green colour.
Bile is stored and concentrated in the gallbladder. The presence of fats in the gut during meals stimulates the gallbladder to empty.
Functions of bile:
- Bile enters the duodenum emulsifying fats into smaller globules, which can then be broken down further by lipase enzymes.
- Metabolic wastes (Cholesterol, phospholipids and electrolytes) and drug products may form part of the bile which can then be excreted from the body through the digestive tract in the faeces.
- Bilirubin, the toxic end product of haemoglobin breakdown, is excreted from the body in this way.
Q.3 iv) Describe the mechanism of digestion and absorption of food in the small intestine.
The small intestine is about 17 feet long. The food from the stomach becomes thoroughly liquefied, it passes into the duodenum, the first segment of the small intestine. Food typically takes 4-5 hours to pass through the stomach into the duodenum, the first part of the small intestine. After being churned and mixed with digestive juices in the stomach, food chyme moves slowly into the folds of the small intestine through the pyloric sphincter or valve. Chyme from the stomach is propelled through the small intestine by peristalsis.
Parts of the small intestine:
The small intestine (or small bowel) is the longest section of the digestive tract and is divided into three segments:
- 1. Duodenum
- 2. Jejunum
- 3. Ileum
Digestive function of the small intestine:
The small intestine consists of three parts in which digestion takes place step by step. The small intestine is where most chemical digestion takes place;
- Peptides (complex chains of protein molecules) are broken down into amino acids
- Lipids (fats) are broken down into fatty acids
- Glycerol; and carbohydrates are broken down into simple sugars like glucose.
To accomplish this, chyme is mixed with additional digestive juices including bile from the liver and pancreatic juice and amylase from the pancreas, as well as other intestinal enzymes such as maltase, lactase and sucrase to break down the chyme and assist in nutrient absorption.
Absorbed nutrients flow in the bloodstream to the liver where they are further metabolized and then either stored or sent to cells in other parts of the body. In total, food typically takes 4-5 hours to transit all three sections of the small intestine. Along with the way, its consistency changes from porridge (chyme) to a thin watery mixture.
1- Digestive function of Duodenum:
The duodenum continues the process of food breakdown; sub-divided into four segments: the superior, descending, horizontal and ascending duodenum. Inside the duodenal tube, chyme is mixed with fluids from the gallbladder (bile) and pancreas (pancreatic juice). Bile breaks down fat particles into smaller droplets, while pancreatic juice contains enzymes that convert fats into fatty acids and glycerol, and sodium bicarbonate to neutralize stomach acid.
2- Digestive function of Jejunum:
Roughly 4-7 feet in length, the jejunum is where the chemical breakdown of the food chyme is completed. Pancreatic enzymes, along with enzymes produced by the jejunum wall, finalize the food digestion process.
3- Digestive function of Ileum:
Roughly 7-5 feet in length, the ileum is the final section of the small intestine, linked to the large intestine by the ileocecal valve. The main function of the ileum is to absorb nutrients. Bile is also absorbed here and returns to the liver through blood vessels in the intestinal walls. The unabsorbed watery remains of the food chyme now pass into the large intestine for water removal and final processing, before being expelled from the body.
Absorption of nutrients in the small intestine:
Inside the small intestine, most of the nutrients are absorbed.
Rugae and Villi:
Although the small intestine has a relatively small diameter, the intestinal walls are covered in wrinkles called rugae, which are themselves covered in millions of finger-like projections called villi, which are themselves studded with millions of smaller projections called microvilli. This provides a surface area of about the size of a tennis court for nutrient absorption.
Structure of villi:
Inside each villus are a series of lymph vessels (lacteals) and blood vessels (capillaries).
The lacteal lymph vessel absorbs digested fat into the lymphatic system which eventually drains into the bloodstream.
The blood vessels receive other nutrients and transport them via the hepatic portal vein to the liver. Here the blood is filtered, toxins are removed and the nutrients are processed.
The function of the liver of absorbed food from small intestine:
An important task performed by the liver in the regulation of blood glucose levels to provide sufficient energy for the body. Excess glucose is converted in the liver to glycogen in response to the hormone insulin and stored. When blood glucose levels begin to drop, (eg. between meals), the glycogen is re-converted to glucose in response to messages conveyed by the hormone glucagon.
Q.3 v) Explain the symptoms and treatment of bulimia nervosa?
“Bulimia nervosa is an emotional disorder characterized by a distorted body image and an obsessive desire to lose weight, in which bouts of extreme overeating are followed by fasting or self-induced vomiting or purging.”
Bulimia nervosa is an eating disorder in which a person may eat a lot of food at once and then try to get rid of the food by vomiting, using laxatives, or sometimes over-exercising. People with bulimia are preoccupied with their weight and body image. Bulimia is associated with depression and other psychiatric disorders and shares symptoms with anorexia nervosa, another major eating disorder. Because many individuals with bulimia can maintain a normal weight, they can keep their condition a secret for years. If not treated, bulimia can lead to nutritional deficiencies and even fatal complications.
Signs and Symptoms of bulimia nervosa:
- Binge eating of high-carbohydrate foods, usually in secret.
- Exercising for hours
- Eating until painfully full
- Damaged tooth enamel, bad breath, sore throat or mouth sores
- Irregular menstruation or lack of menstrual periods in females
- Constipation, diarrhoea, nausea, abdominal pain.
- Bodyweight that goes up and down
- Going to the bathroom during meals
Treatment of bulimia nervosa:
- Psychotherapy is a cornerstone of bulimia treatment. Cognitive behavioural therapy which teaches to replace negative thoughts and behaviours with healthy ones is often used.
- Other mind-body and stress-reduction techniques, such as yoga, tai chi and meditation, may help a person to become more aware of your body and form a positive body image. The person with bulimia nervosa needs to be actively involved in their treatment.
- Antidepressants are often prescribed for bulimia nervosa.
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